Hello Michael,
Last summer I moved from a Windows PC to a 24" M1 iMac. I am delighted.
I have LR and PS on subscription and so have the latest versions. Both work as you would expect and the machine is so much faster. I have external hard drives formatted as exFAT so they will read on both PCs and Macs. I use two Sandisk portable SSDs alternately for Time Machine. They come with both USB A and USB C connectors. After the first run which took a while, Time Machine is very quick, usually some 5 to 10 minutes.
I have a 16GB, 1TB version and the SOC seems to make it run very well. My biggest image is almost square and is the result of 9 images stitched with PtGui. It is about 100MP and the 16-bit TIFF is 1GB. I handles like any other image in LR. I do not do video processing so can't comment on that.
All my images, apart from current ones are on external HDs and SSDs and that's fine. My LR catalogue (38k images) is on the internal SSD. My only issue was with the Canon Print and Layout plug-in for my Canon Pro-300 printer. I did have an old 9500MK2, but Canon no longer do current drivers for it The plug-in worked fine from LR but would not appear in PS. Canon were perplexed. It all magically sorted when Adobe released a bug fix for PS. I have M1 profiles for my papers.
As I wrote earlier, I am delighted.
Best wishes,
Jonathan